1. Field of the Invention
The present invention relates to a heating apparatus in which a heating member is supported by a heat-insulating material and, more particularly, to a heating apparatus mainly suitable for use in a semiconductor manufacturing process.
2. Description of the Related Art
In a process for manufacturing a semiconductor, e.g., a transistor and an IC, a diffusion furnace, in which a furnace core tube is surrounded by a cylindrical member constituted by a heat-insulating material and a heating coil is supported on the inner surface of the cylindrical member, is conventionally often used as a heating apparatus for diffusing impurities on the silicon substrate.
The cylindrical member for supporting the heating coil is constituted by heat-insulating bricks. Recently, in order to reduce the size and weight of the apparatus and to minimize external heat dissipation, a product mainly containing, e.g., an alumina fiber having a bulk density of 0.3 g/cm.sup.3 and a small heat conductivity is often used as the material of the cylindrical member.
Although the alumina fiber is optimum as the heat-insulating material of the diffusion furnace, since its bulk density is large, its heat capacity is large, and it takes a long period of time to increase or decrease the temperature in the furnace. As the diameter of a semiconductor wafer is increased (e.g., from 4 inches to 6 inches and then to 8 inches), the size of the heating apparatus is also increased, and the weight of the heating apparatus is also increased Hence, it is demanded to reduce the weight of the heating apparatus.